1. Field of the Invention
This invention relates to a heat exchanger fin with louvers having an extended length and to a roll forming tool for use in manufacturing such louvers. More specifically, the present invention relates to a roll forming tool for manufacturing such louvers on a heat exchanger that utilizes physical media to either extract heat or cold from a source.
2. Background Art
It is generally known that a layer or film of fluid of indefinite thickness exists when a heat- or cold-transferring fluid contacts with a surface having a different thermal energy than the fluid. That layer is in direct contact with the heating surface, to which it tends to adhere and form a relatively thermally insulating covering. That covering reduces the rate of transfer of thermal energy. Such adherence is explained by friction between the fluid and the surface which causes the layer to move more slowly in relation to the more remote layers of fluid which may pass relatively unencumbered over the adherent layer. Such phenomena tend to diminish the efficiency of a heat exchanger. As a result, prior art heating approaches have used relatively large areas of heating surface in order to heat a fluid to a desired temperature.
Broadly stated, these prior art approaches have addressed the problem by disturbing this essentially non-conductive layer and enabling most of the fluid to be heated or cooled to come into direct contact with the heating or cooling surface respectively by modifying the surface. Such approaches, however, have been only somewhat effective in raising the efficiency of a heat exchanger.
The surface over which the heat transfer occurs is called a fin or louver. The louver deflects or directs the air and channels heat or coldness from a source. In existing louver designs, little turbulence actually occurs and laminar flow is relatively uninterrupted. These louvers or fins are commonly used to deflect air in conventional heat exchangers. Other uses for such structures have included deployment in air filters, air deflectors, structural spacers, noise reducers, and some components for electrical devices. Other details of the louvers and their characteristics are disclosed in commonly owned U.S. Pat. Nos. 5,682,784 and 5,738,169 which are hereby incorporated by reference.
The louvers or fins are typically produced by a roll forming tool called a finroll. Existing roll finrolls include a set of rolls which are each part of a rotating assembly. They are designed so that when they are mated and rolled in unison with each other, they produce a louvered serpentine fin from a strip of material that is introduced into the mating area of the finrolls. Existing finrolls are made up of a series of differently shaped blades or disks which are characterized by an outer peripheral shape and thickness. The thickness of each blade is a variable and is determined usually by the width of the louver that is to be manufactured. The outer perimeter of the disk is used to either preform or finish form the serpentine shape. It is also known to provide an offset on non-symmetrical blade flanks on the finroll to compensate for unequal rolling stresses induced into the fins.